1. Technical Field
The present invention generally relates to structures of window coverings, and more particularly to a control structure for raising and lowering a window covering.
2. Description of Related Art
A conventional window covering includes a headrail, a bottom rail, and a shade material located between the headrail and the bottom rail, and at least two lifting cords pass through the shade material. The window covering further includes a control structure, which rotates a shaft to roll up or release the lifting cords to collapse or expand the shade material.
Such conventional control structure uses a ratchet, which provides a clutch function, to rotate the shaft provided in the headrail forwards or backwards, and consequently, the lifting cords wound around the shaft are pulled or released to collapse or expand the shade material. However, during the process of controlling the control structure to collapse or to expand the shade material, the components of the ratchet tend to collide with each other and generate disturbing noise.
In addition, the conventional ratchet includes a pawl having a sloped surface, while each tooth of the corresponding gear also has a sloped surface, so that the pawl and the gear can either mesh or interlock with each other, whereby the ratchet only has one permitted direction. However, the pawl in this kind of structure is usually turned by gravity. In other words, the pawl could be reversely turned, while the pawl is rotated forwards or backwards, or stays at a lower position, such that the conventional ratchet is not reliable.